Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.
BuiltWith - Find out the technology behind websites
Whoisology - Connected database of whois records and whois history
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.
JSON WHOIS API - Parsed domain WHOIS data from any WHOIS server via RESTful API with metered pay as you pricing.